/*
 * Copyright (c) 2024, Alibaba Cloud;
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.aliyun.dataworks.migrationx.transformer.core.sqoop;

import java.rmi.server.UID;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Securely generate random MD5 signatures for use as nonce values.
 */
public final class RandomHash {

    private RandomHash() {
    }

    /**
     * Generate a new random md5 hash.
     *
     * @return a securely-generated random 16 byte sequence.
     */
    public static byte[] generateMD5Bytes() {
        try {
            MessageDigest digester = MessageDigest.getInstance("MD5");
            long time = System.currentTimeMillis();
            digester.update((new UID() + "@" + time).getBytes());
            return digester.digest();
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * Generate a new random md5 hash and convert it to a string.
     *
     * @return a securely-generated random string.
     */
    public static String generateMD5String() {
        byte[] bytes = generateMD5Bytes();
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            int x = ((int)b) & 0xFF;
            sb.append(String.format("%02x", x));
        }
        return sb.toString();
    }
}
